This thesis presents an exploration of π-conjugation effects in two previously known small macrocycles, [18]annulene and [24]paracyclophanetetraene and the synthesis of new, large nanorings built of porphyrin subunits.

Chapter 1 introduces the reader to the field of aromatic macrocycles and to the concept of aromaticity. It is then followed by an overview of basic synthetic methods useful in the synthesis of macrocycles.

Chapter 2 describes the red-ox behaviour of [18]annulene, an archetypal annulene and one of the iconic molecules of organic chemistry. The highly reactive anions of [18]annulene are explored both in solution using NMR methods and in the solid state using single crystal X-ray diffraction. The results show that the [18]annulene dianion has a different geometry than described 50 years ago. The reduction can go further and the tetraanion forms a sandwich-type dimer observed both in solution and in the solid state.

Chapter 3 explores the structural manifestation of (anti)aromaticity in the solid-state structures of anions of [24]paracyclophanetetraene in various coordination environments.

Chapter 4 reports the synthesis of a phenylene-linked porphyrin nanoring built of edge-fused porphyrin dimer units. It demonstrates that fusion of porphyrins can be performed even on highly strained systems.

Chapter 5 describes the synthesis of a giant spoked 18-porphyrin nanoring, the first example of 5,15-linked porphyrin nanoring with direct bonds (and no spacer) between the porphyrin units.

Listed in the Appendix is an overview of the crystal structures obtained during the DPhil studies, resulting from X-ray measurements and refinements that I performed both for my compounds and for these obtained by other group members for their projects.